Data required to be shown on floodplain zoning maps

Data required to be shown on floodplain zoning maps.

Data required to be shown on floodplain zoning maps. Municipalities shall delineate the entire floodplain on their floodplain zoning maps.

(1) If the regional flood profile has been determined, the profile shall be used to develop the floodplain zoning maps which the municipality shall use as the basis for floodplain zoning.

(a) The maps shall show the following:

1. The floodway district;

2. The floodfringe district;

3. The regional flood elevation consistent with the regional flood profile shall be clearly lettered at identifiable positions on the official floodplain zoning maps. If for any reason that elevation is not shown on the maps, the profile shall be attached to and made a part of the maps; and

4. Source and date of study.

(b) In addition to the information in par. (a) , the floodplain zoning maps shall include the following information, where applicable:

1. The shallow depth flooding district.

2. The flood storage district.

3. The coastal floodplain district.

4. Floodplain islands.

5. For developed and undeveloped areas downstream of dams, the floodway and floodfringe districts based on 3 conditions:

a. Assuming the dam is in place,

b. Assuming the dam is not in place, and

c. Assuming failure of the dam during the regional flood.

6. For areas adjacent to levees, floodwalls and channel improvements, the floodway and floodfringe districts based on 2 conditions:

a. Assuming the levee, floodwall or channel improvement is not in place, and

b. Assuming the levee, floodwall or channel improvement is in place.

ng the dam is in place,

b. Assuming the dam is not in place, and

c. Assuming failure of the dam during the regional flood.

6. For areas adjacent to levees, floodwalls and channel improvements, the floodway and floodfringe districts based on 2 conditions:

a. Assuming the levee, floodwall or channel improvement is not in place, and

b. Assuming the levee, floodwall or channel improvement is in place.

(c) If technical information is available to ascertain the magnitude of floods larger than the regional flood the floodplain limits of these large floods may be reflected on the official floodplain zoning maps and used for either public information purposes or for regulation.

(2) If the regional flood profile has not been determined, maps based upon historical floods, flood prone area maps, flood hazard boundary maps, aerial photos or detailed soils maps may initially serve as a basis for floodplain delineation, provided that the associated text of the zoning ordinance provides for a procedure similar to ss. NR 116.20 (2) and 116.21 (3) to ascertain the effects of all development upon flood flows and the regional flood elevation.